The parent of United Airlines reported a first-quarter loss that more than doubled from a year ago thanks to costs related to integrating Continental Airlines.

United Continental Holdings said it had a $448 million net loss, or a $1.36 loss per share, in the first three months of the year, not as bad as analysts expected.

Excluding $162 million in charges mainly linked to the integration costs, the loss amounted to $286 million, or 87 cents per share, UAL said. The Wall Street average estimate was for a $1.03 loss per share.

"This was a difficult quarter, but we made significant progress with our integration and we're now able to serve our customers as a single airline," said Jeff Smisek, UAL president and chief executive, in a statement.

Smisek said that UAL was looking forward to "delivering more benefits from the merger in the remainder of the year."

The world's biggest airline also was hit by rising fuel prices, a major driver of a 8.6 percent increase in operating costs.

"Our revenue results were negatively impacted by the integration of our revenue management and booking systems, which included reducing our booking levels so we could better serve our customers during the reservations conversion," said Jim Compton, UAL's executive vice president and chief revenue officer.

In late November UAL received US Federal Aviation Administration approval for a single operating certificate for United and Continental after an 18-month process of aligning the two airlines' operating policies and procedures.

United Continental Holdings was formed in 2010 by the merger of United and Continental.

Shares in UAL were down 1.5 percent at $22.63 in morning trade in New York.